1. Field of the Invention
The present invention relates to a roll stand for use in a continuous polymer web extrusion line, and more specifically to a roll stand having an auxiliary section shiftable in relation to a primary section.
2. Description of the Background of the Invention
During the process of extruding a molten polymer web, it is customary to feed the extrudate into a roll stand having at least one primary chilled roll in order to cool the extrudate below a solidification temperature thereof. Under certain conditions such as high extrusion velocities, it may be desirable to have one or more auxiliary chilling rolls in order to attain the desired cooling. Under such circumstances, it is often convenient to shift the auxiliary rolls away from or toward the primary roll during the start up process of a new web and then re-adjust the distance between the primary and auxiliary rolls after the web is sufficiently stable.
Nissel U.S. Pat. No. 6,575,726 discloses a roll stand for use in a polymer web extrusion line including a slot extrusion die, a primary roll stack, a plurality of auxiliary rolls, and a pair of draw rolls. The auxiliary rolls are laterally shiftable in relation to the primary roll stack in order to provide adjustability. A mechanical linkage connects the auxiliary rolls to each other in order to maintain a constant spacing therebetween when the auxiliary rolls are shifted in relation to the primary rolls.
However, when shifting the rolls in relation to each other while a web is passing thereover, it is usually necessary to adjust the rotational velocity of each roll during the movement in order to prevent sagging or bunching of the web on either side of the rolls being shifted. It is desirable to have a simple and efficient method of minimizing the amount of adjustment to the rotational velocity of the various rolls in a roll train in order to facilitate start-up adjustments or to perform maintenance on portions of the roll stand while the web is being passed therethrough.